1. Technical Field
The present invention relates to a more environmentally friendly cement for bonding and/or sealing carbon articles such as monolithic carbon foams useful for applications including as composite tooling material. More particularly, the present invention relates to a process and material for cementing together carbon foam articles to permit the formation of functionally-acceptable larger articles or for sealing the surface of blocks of carbon foams to provide a working surface thereon or to permit surfaces of two articles of foam to be cemented together to form larger articles.
2. Background Art
Carbon foams have attracted considerable interest recently because of their properties of low density, coupled with either very high or low thermal conductivity. Indeed, in their U.S. Pat. No. 6,849,098, Joseph and Rogers describe the use of a carbon foam product as tooling for the production of composite materials. Unfortunately, the foams produced by the processes of the Joseph and Rogers patent are unsuitable for use as tooling without the addition of a layer of a so-called facesheet material, because of the pore structure of the foams, including the open-celled nature with highly interconnected pores. The use of such facesheet materials, however, results in either completely or partially filling of the foam cell volume in the Joseph and Rogers disclosure. Filling of cells with these facesheet materials will raise the density and reduce the effectiveness of the foam as a lightweight material for use in composite tooling. In addition, the use of these facesheets creates difficulties in adhesion and in terms of lack of thermal expansion compatibility. Also, the Joseph and Rogers foam products likely do not have the required strength to density ratios needed for tooling and other structural applications, and cannot be produced in sufficiently large blocks for tooling, thus requiring several blocks to be cemented together; while cementing of blocks together can and is successfully done, the more cemented joints that are present, the less structural integrity the resulting block will have.
Recently, a carbon foam has been developed and commercialized under the trademark GRAFOAM by UCAR Carbon Company Inc. of Parma, Ohio and described by Miller, Lewis, and Mercuri in U.S. Patent Publication No. 20060086043. This foam is monolithic and has a controllable cell structure, where the cell structure, strength, and strength to density ratio make the foam suitable for use as composite tooling as well as in other applications. Indeed, a combination of characteristics found in GRAFOAM carbon foam, including strength to density ratios higher than contemplated in the prior art, have been found to be desirable for use of a carbon foam in composite tooling applications.
Cements for carbon bodies have been disclosed in the past. For instance, in U.S. Pat. No. 5,002,981, Chiu discloses a carbonaceous cement paste composition having carbonaceous particles and a resin binder system composed of a high-temperature polymeric resin binder and a thermosettable furfuryl alcohol for dissolving the resin, and a heat-activated catalyst for effecting thermosetting of the furfuryl alcohol upon heating. The carbonaceous particles disclosed by Chiu include graphite flour, coke flour, carbon black, pitch coke flour and calcined lampblack flour. The carbonaceous particles are present at from about 20% to about 85% by weight.
Likewise, in U.S. Pat. No. 6,214,158 to Chiu, Lewis, and Lewis, a cement paste composition is disclosed, including a catalyst, a carbon filler present in an amount of about 20 to about 60% by weight, a polymerizable monomeric system, and a furan solvent. The curable cement composition may be used along with a pre-coat in an adhesive system for attaching together carbon bodies. The carbon filler can be pitch coke flour, petroleum coke flour, graphite powder, coal, carbon black or mixtures thereof.
In U.S. Pat. No. 5,280,063, Lewis, Pirro, Greinke, Bretz, and Kampe disclose a room temperature setting carbonaceous cement comprising a solid carbonaceous material, a catalyst and a liquid carbonizable component which when treated with the catalyst will provide a carbon yield of at least 40% at an elevated baking temperature and possess a flexural strength which is above at least 750 psi at room temperature and at said elevated temperature.
Tyler, in his U.S. Pat. No. 3,441,529, discloses a thermosetting cement for bonding carbonaceous structures, having a mixture of an oil, a soap, finely-divided carbonaceous particles, furfuryl alcohol, a phenolic novolac resin, and a hardening agent.
Furthermore, U.S. Patent Publication No. 20060159905 discloses a sealant material which effectively fills the relatively small cells and bimodal cell structure of the carbon foam of Miller, Lewis, and Mercuri. In addition, the sealant disclosed can seal the mating surfaces of two carbon foam articles so as to permit carbon foam blocks to be cemented together.
Although the prior art discloses various cements useful for carbon articles including carbon foam, many cements pose environmental or health and safety problems. Specifically, cements containing furfuryl alcohol or furfuraldehyde possess a strong odor which evolves during the application and curing of the cement. As such, both the bonding and the cementing of carbon foam articles can be quite unpleasant or unhealthful when conducted in an enclosed space.
What is desired therefore, is a material useful for both cementing and sealing carbon bodies, especially carbon foams whose pore structure, strength, and strength-to-density ratio is suitable for use in applications such as composite tooling, wherein the cementing material does not contain furfuryl alcohol or furfuraldehyde. Also desired is a method for producing such cement.